Well, off the top of my head, here's a few choices.
Battle for Middle-Earth: Never played the second one but the original was actually pretty neat if you could get used to the unusual base-building scheme they pioneered at the time, which other games like Company of Heroes later pilfered from (and mostly improved upon). Granted, the factions were kind of poorly balanced (Gondor dominated most of the time unless you managed to spam Rohirrim Riders as Rohan to quite literally steamroll everyone else. Isengard was difficult to master and Mordor just kind of sucked until you got some higher-tier units).
Jedi Outcast: Contrary to what some might conclude, I don't think the Jedi Knight games have the best lightsaber combat ever. In fact, the idea of marrying lightsaber attacks to player movement and making blocking a randomized thing completely out of the player's control just ended up making the entire thing a spamfest most of the time (ironically, I think a system like Mordhau's is what they should have originally gone with, assigning slashing, stabbing and blocking to mouse movement). I do, however, think that Jedi Outcast had some really fun level design which really made you use all the tools at your disposal to survive, instead of just relying on one superior method. It felt like the last gasp of the 90s in a way, even though the game came out in 2002.
Prince of Persia - Warrior Within: Fuck you, I liked it. It probably had the best plot of the trilogy, Kaileena was way better than Farah, the Dahaka chase sequences were pretty cool and the combat system was damn neat for the time and most fluid of all the games. Pity that The Two Thrones basically pissed away the potential of the ending but that's Ubisoft for you. That being said, the Godsmack soundtrack was horrible and the level design and the endless backtracking got annoying pretty quick.
Dark Messiah of Might and Magic: It's a classic. It feels like Half-Life but in a sword and sorcery setting and it sells it well. Combat system was actually pretty bare-bones and it's obvious Arkane didn't get to flesh it out as much as they wanted to. What killed it in sales was Ubisoft stupidly marketing it as an RPG when it was really a First Person Swashbuckler. Another issue is that it's way too short. It need at least another 4 chapters.
Batman - Arkham Asylum: Only game in the series that really was fun and didn't take itself too seriously. Best atmosphere, rather simple plot but miles ahead of the convoluted bullshit that was Arkham City and Arkham Knight, second best sound design, best soundtrack and juuust open-world enough so it feels full of content, instead of being mostly large empty areas populated by some buildings and thugs. It doesn't try to build some unique continuity (again, fuck off Arkham City), it just assumes awareness of mainstream Batman continuity and throws you right in for a fun adventure.